Radioisotope production o-18 water target having improved cooling performance

ABSTRACT

A target apparatus for producing a radioisotope having improved cooling performance including a cavity member including a cavity accommodating H 2   18 O concentrate and producing  18 F through a nuclear reaction between the H 2   18 O concentrate and protons irradiated onto the H 2   18 O concentrate, wherein the cavity member includes a front aperture and a rear aperture disposed in opposite directions on a path in which the protons are irradiated and connected to the cavity so that the cavity has openings. wherein a thermo-chemically stable layer plated with titanium or niobium is formed in an inner circumference of the cavity.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2009-0044118, filed on May 20, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radioisotope O-18 water (H₂ ¹⁸O) target apparatus having improved cooling performance in order to reduce heat generated and pressure increase in a cavity when a high current of given energy of protons is irradiated to produce a radioactive isotope F-18 through a nuclear reaction between the protons and the O-18 water (H₂ ¹⁸O).

The present invention is derived from a research project supported by the Atomic Energy Research & Development (R&D) Program of the Ministry of Education, Science, and Technology [M2070605000108M060500110, Development of Superconducting Cyclotron Main Technology].

2. Description of the Related Art

In general, positron emission tomography (PET) is widely used in early diagnosis of tumors and various diseases.

PET has recently been able to diagnose more diseases through development of a variety of positron emission radio-isotope marked medicines. Representative positron emission radio-isotope marked medicines are FDG (2-[18F]Fluoro-2-deoxy-D-glucose) used to diagnose a cancer and L-[11C-methyl]methionine used to diagnose a brain tumor.

FDG may be produced by irradiating protons onto O-18 water (H₂ ¹⁸O), producing a radioactive isotope F-18 through a ¹⁸O(p,n)¹⁸F nuclear reaction, and chemically combining the radioactive isotope F-18. Therefore, an apparatus for producing the radioactive isotope F-18 is needed, and thus a O-18 water (H₂ ¹⁸O) target apparatus may be used.

The amount of radioactive isotope F-18 produced by the O-18 water (H₂ ¹⁸O) target apparatus is indicated as a yield. The yield of the O-18 water (H₂ ¹⁸O) target apparatus during a nuclear reaction is proportional to the number of protons, which may be expressed as a proton current, at a given energy thereof measured in electron volts eV. The total energy of the protons is expressed as a product of the unit energy of the protons and the number of protons. However, only a part of the energy of the protons is used for the nuclear reaction, and most of the remaining energy of the protons is converted into heat. Thus, if the current or respective energy of protons thereof is increased so as to increase the yield of the O-18 water (H₂ ¹⁸O) target apparatus, the O-18 water (H₂ ¹⁸O) target apparatus absorbs a greater amount of energy, which may involve a nucleation in the O-18 water (H₂ ¹⁸O) in a cavity, such that the cavity has increased temperature and pressure. Such conditions unfavorably influence the life span of the O-18 water (H₂ ¹⁸O) target apparatus. In more detail, a density fluctuation of the O-18 water (H₂ ¹⁸O) is partially cased by a nucleation inside the cavity which varies the nuclear reaction rate and reduces the yield of the O-18 water (H₂ ¹⁸O) target apparatus.

Therefore, it is important to increase the cooling efficiency of the O-18 water (H₂ ¹⁸O) target apparatus in order to increase the life span and production yield of the O-18 water (H₂ ¹⁸O) target apparatus.

SUMMARY OF THE INVENTION

The present invention provides a target apparatus having an improved structure for an effective cooling of O-18 water in a cavity during a nuclear reaction.

According to an aspect of the present invention, there is provided a radioisotope production target apparatus having improved cooling performance including a cavity member including a cavity accommodating O-18 water and producing F-18 through a nuclear reaction between the H₂ ¹⁸O concentrate and protons irradiated onto the O-18 water, wherein the cavity member includes a front aperture and a rear aperture disposed in opposite directions on a path in which the protons are irradiated and connected to the cavity so that the cavity has openings, the target apparatus including: a front membrane disposed to cover the front aperture; a rear cover disposed to cover the rear aperture; a front cooling member coupled to the cavity member to support the front membrane so as to prevent the front membrane from swelling due to an pressure increases in the cavity during the nuclear reaction, disposed on the path in which the protons are irradiated, and including a plurality of through holes extending in a direction the protons are irradiated; a central cooling member including a space for supplying cooling water around the cavity and coupled to the cavity member; and a rear cooling member coupled to the rear cover and allowing the cooling water to be supplied, wherein a thermo-chemically stable layer plated with titanium or niobium is formed in an inner circumference of the cavity.

The thickness of the thermo-chemically stable layer may be between about 1 μm and 10 μm.

The cavity may be between about 5 mm and about 20 mm long along the path in which the protons are irradiated.

The cavity may have a truncated cone shape having an inner diameter increasing from an upstream side to a downstream side along the path in which the protons are irradiated.

The cavity member may include a plurality of first cooling fins that protrude from an exterior surface of the cavity, extend around the circumference of the cavity, and are spaced apart from each other in the direction in which the protons are irradiated.

The rear cover may include a plurality of second cooling fins that protrude toward the cavity, extend in a direction perpendicular to a ground, and are spaced apart from each other in a direction perpendicular to the direction perpendicular to the ground.

The target apparatus may further including: a plurality of through holes having circular or hexagonal cross sections perpendicular to the path in which the protons are irradiated, and arranged in a honeycomb shape and having cross sections perpendicular to the path in which the protons are irradiated.

The front membrane may be formed of titanium or niobium.

The plurality of second cooling fins may be plated with titanium or niobium.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a schematic perspective view of a target apparatus, according to an embodiment of the present invention;

FIG. 2 is an enlarged cross-sectional view of a portion “A” of FIG. 1;

FIG. 3 is an enlarged view of a portion “B” of FIG. 1;

FIG. 4 is a cross-sectional view of the target apparatus of FIG. 1;

FIG. 5 is an enlarged cross-sectional view of a portion “C” of FIG. 4;

FIG. 6 is an exploded perspective view of the target apparatus of FIG. 1, viewed from a first direction for explaining the main elements;

FIG. 7 is an enlarged view of a portion “D” of FIG. 6;

FIG. 8 is an enlarged view of a portion “E” of FIG. 6;

FIG. 9 is an exploded perspective view of the target apparatus of FIG. 1, viewed from a second direction; and

FIG. 10 is an enlarged view of a portion “F” of FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

FIG. 1 is a schematic perspective view of a O-18 water (H₂ ¹⁸O) target apparatus 10 (hereinafter, referred to as “target apparatus”), according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a portion “A” of FIG. 1. FIG. 3 is an enlarged view of a portion “B” of FIG. 1. FIG. 4 is a cross-sectional view of the target apparatus 10. FIG. 5 is an enlarged cross-sectional view of a portion “C” of FIG. 4. FIG. 6 is an exploded perspective view of the target apparatus 10, viewed from a first direction for explaining the main elements. FIG. 7 is an enlarged view of a portion “D” of FIG. 6. FIG. 8 is an enlarged view of a portion “E” of FIG. 6. FIG. 9 is an exploded perspective view of the target apparatus 10, viewed from a second) direction. FIG. 10 is an enlarged view of a portion “F” of FIG. 9.

Referring to FIGS. 1 through 9, the target apparatus 10 for producing a radioisotope and having improved cooling performance may produce a radioactive isotope ¹⁸F through a nuclear reaction between protons irradiated onto an H₂ ¹⁸O concentrate and the H₂ ¹⁸O concentrate. An arrow “Y” shown in FIG. 4 indicates an inlet through which cooling water is injected. An arrow “Z” shown in FIG. 4 indicates an outlet through which the cooling water is discharged. An arrow “S” shown in FIG. 5 is a direction of O-18 circulation in which the O-18 water is circulated by convection during proton irradiation.

The target apparatus 10 includes a cavity member 20, a front membrane 30, a rear cover 40, a front cooling member 50 , a central cooling member 60, and a rear cooling member 70.

The cavity member 20 includes a cavity 22, a plurality of first cooling fins 23, a front aperture 24, and a rear aperture 25. The cavity member 20 is formed of a metal having excellent thermal conductivity, such as copper Cu.

The cavity 22 is formed in the center of the cavity member 20. The cavity 22 is filled with the O-18 water. A thermo-chemically stable layer that is plated with titanium Ti or niobium Nb is disposed on an inner circumference of the cavity 20. The thermo-chemically stable layer effectively transfers heat generated from the O-18 water of the cavity 22 to an exterior of the cavity 22, provides better cooling efficiency than in case cavity member is made only with Ti of Nb, and maintains the O-18 water of the cavity 22 in a chemically stable state. Thickness of the thermo-chemically stable layer may be between about 1 μm and 10 μm. If the thickness of the thermo-chemically stable layer is below 1 μm, the target apparatus 10 may not maintain chemical stability of the O-18 water during the nuclear reaction. Meanwhile, if the thickness of the thermo-chemically stable layer exceeds 10 μm, the chemical stability of the target apparatus 10 may be improved, but since titanium Ti or niobium Nb, which are expensive materials, is used, manufacturing costs increases accordingly and the cooling performance will gradually decreases.

The cavity 22 is open at the front aperture 24 and the rear aperture 25. The cavity 22 has a circular cross-section with regard to a plane perpendicular to a path in which the protons are irradiated. In more detail, the cavity 22 is a truncated cone shape having an inner diameter that increases from an upstream side of to a downstream side of the path in which the protons are irradiated. The truncated cone shape of the cavity 22 is used to increase a surface area of the cavity 22 as great as possible that is thermally exchanged with the first cooling fins 23. The volume of the cavity 22 is approximately 1.5 cc, which is generally the optimized amount used for the nuclear reaction involving the H₂ ¹⁸O concentrate. The O-18 water is expensive and thus reduced usage may be desired. The cavity 22 may be between about 5 mm and about 20 mm long along the path X in which the protons are irradiated. If the length of the cavity 22 is below 5 mm, space for the second cooling fins 42 is reduced, making it difficult to effectively improve the cooling performance of the target apparatus 10. Meanwhile, if the cavity 22 exceeds 20 mm, the volume of the cavity 22 unnecessarily increases.

The first cooling fins 23 protrude from an exterior surface of the cavity 22. The first cooling fins 23 extend around the circumference of the cavity 22. The first cooling fins 23 are spaced apart from each other in the direction in which the protons are irradiated. The first cooling fins 23 contact the cooling water so that a heat exchange occurs. The first cooling fins 23 increase an area of contact with the cooling water when the heat exchange occurs between the first cooling fins 23 and the cavity 22, thereby increasing efficiency of the heat transfer.

The front aperture 24 and the rear aperture 25 are disposed facing each other on the path in which the protons are irradiated, and surrounding the cavity 22. The front aperture 24 and the rear aperture 25 are connected to the cavity 22 so that the cavity 22 may have openings.

The protons are irradiated toward the cavity 22 through the front aperture 24 so that energy of the irradiated protons may be entirely absorbed in the O-18 water of the cavity 22.

The front membrane 30 and the rear cover 40 are disposed to cover the front aperture 24 and the rear aperture 25, respectively. The O-18 water does not externally flow out from the cavity 22 due to the front membrane 30 and the rear cover 40, and the cavity 22 is continuously filled with the O-18 water. The front membrane 30 and the rear cover 40 are coupled to the cavity 22 using a sealing member (not shown) such as polyethylene.

The front membrane 30 is formed of a metal, such as titanium Ti or niobium Nb, and its thickness is generally several tens of micrometers. In the present embodiment, the thickness of the front membrane 30 is 50 μm.

The rear cover 40 includes a plurality of second cooling fins 42 and a plurality of third cooling fins 44. The second cooling fins 42 protrude toward the cavity 22. The second cooling fins 42 extend in a direction perpendicular to a ground. The second cooling fins 42 are spaced apart from each other in a direction perpendicular to the direction perpendicular to the ground since the O-18 water filled in the cavity 22 flows down in the direction perpendicular to the ground from an upper side of the second cooling fins 42 to a lower side thereof due to a change in the density of the O-18 water during the nuclear reaction as shown in FIG. 5, thereby achieving greater cooling performance. The second cooling fins 42 are plated with titanium Ti or niobium Nb, that is, the same metal as the thermo-chemically stable layer.

Referring to FIG. 10, the third cooling fins 44 protrude in a direction opposite to the protrusion direction the second cooling fins 42, between a wall surface of the rear cover 40. In more detail, the third cooling fins 44 directly contact the cooling water injected into a third space 72 so that heat exchange therebetween may occur.

The rear cover 40 and the rear cooling member 70 form the third space 72 in which the cooling water flows.

The front cooling member 50 is coupled to the cavity member 20 to support the front membrane 30. The front membrane 30 is disposed between the front cooling member 50 and the cavity member 20. The front cooling member 50 includes a plurality of through holes 52. The through holes 52 are formed penetrating the front cooling member 50 due to a plurality of front lattice portions 53 along the path in which the protons are irradiated. The total area of the through holes 52 occupies 80% or more of the total area of the front aperture 24. Protons that do not enter the through holes 52 of the front cooling member 50 cause a loss of energy. Therefore, if the total area of the through holes 52 is below 80% of the total area of the front aperture 24, a great amount of energy of the protons may be lost, which reduces production efficiency of F-18. The through holes 52 may have circular or hexagonal cross sections perpendicular to the path in which the protons are irradiated. The through holes 52 may be arranged in a honeycomb shape and have cross sections perpendicular to the path in which the protons are irradiated. A ring shape first space 54 in which the cooling water flows is formed in the front cooling member 50. An inlet into which the cooling water is injected is formed in one side of the first space 54, and an outlet in which the cooling water is discharged is formed in the other side thereof. When the protons are irradiated, heat generated from the front lattices 53 of the front cooling member 50 and heat generated through the nuclear reaction are cooled by the cooling water that flows into the first space 54 through the front lattices 53. The front cooling member 50 may be formed of a metal having good thermal conductivity, such as aluminum Al or copper Cu. The front cooling member 50 supports the front membrane 30 and prevents the front membrane 30 from swelling due to increases in the temperature and pressure of the O-18 water of the cavity 22. The central cooling member 60 includes a second space 62 for supplying the cooling water around the cavity 22. The central cooling member 60 is coupled to the cavity member 20 to prevent the cooling water from being discharged through a sealing member such as polyethylene. The central cooling member 60 includes a path in which the cooling water is injected into the second space 62 and a path in which the cooling water is discharged from the second space 62.

The rear cooling member 70 is coupled to the rear cover 40. The rear cooling member 70 includes the third space 72 in which the cooling water comes in and out and flows, and a path in which the cooling water comes in and out the third space 72. The rear cooling member 70 and the rear cover 40 are sealed by a sealing member such as polyethylene so as to prevent the cooling water from escaping from where the rear cooling member 70 is coupled to the rear cover 40.

The front cooling member 50, the cavity member 20, the rear cover 40, the central cooling member 60, and the rear cooling member 70 are integrally coupled to each other through a coupling member such as a bolt.

Hereinafter, the effect of the present invention will now be described in more detail described by explaining a method of producing F-18 using the target apparatus 10 of the present embodiment. If a cyclotron, for example, a particle accelerator, generates protons having a suitable amount of energy and irradiates the protons to the target apparatus 10, a portion of the protons may not penetrate the front lattice 53 of the front cooling member 50 and another portion may enter the through holes 52 of the front cooling member 50. A portion of the protons that have entered the through holes 52 of the front cooling member 50 is absorbed in the front membrane 30 and another portion is absorbed in the O-18 water of the cavity 22 of the cavity member 20. When the protons are irradiated onto the O-18 water, the protons undergoes a nuclear reaction with the O-18 water, and thus F-18 is produced. Heat generated in the front lattices 53 of the front cooling member 50 is cooled by the cooling water that flows in the ring shape first space 54 of the front cooling member 50. Heat generated during the nuclear reaction between the protons and the O-18 water is cooled by the cooling water that flows in the second space 62 formed by the cavity member 20 and the central cooling member 60.

Meanwhile, a high temperature generated during the nuclear reaction between the protons and the O-18 water is cooled by the cooling water that flows in the second space 62 formed by the cavity member 20 and the central cooling member 60 and also cooled by the cooling water that flows in the third space 72 formed by the rear cover 40 and the rear cooling member 70. During this process, the first, second, and third cooling fins 23, 42, and 44 have large surface areas contacting the cooling water, thereby remarkably increasing the cooling effect. Also, the thermo-chemically stable layer plated in the inner circumference of the cavity 22 quickly transfers heat of the cavity 22 to the first cooling fins 23, thereby maintaining the O-18 water of the cavity 22 at a stable temperature and pressure. In particular, the second cooling fins 42 protrude toward the cavity 22 and have the largest surface contacting the O-18 water of the cavity 22, thereby remarkably increasing the cooling performance of the target apparatus 10.

The cavity 22 is a truncated cone having an inner diameter increasing in the direction in which the protons are irradiated, which increases a surface of the first cooling fins 23 contacting the cooling water, thereby increasing the cooling performance compared to the conventional art.

Although the thickness of the thermo-chemically stable layer may be between about 1 μm and 10 μm in the present embodiment, the present invention is not limited thereto, and the objective of the present invention may be achieved according to the thermo-chemically stable layer.

Although the cavity 22 is a truncated cone having an inner diameter increasing from an upstream side to a downstream side along the path in which the protons are irradiated in the present embodiment, the present invention is not limited thereto, and the objective of the present invention may be achieved according to the thermo-chemically stable layer.

Although the cavity member 20 includes the first cooling fins 23 that extend in around the circumference of the cavity 22 and are spaced apart from each other in the direction in which the protons are irradiated in the present embodiment, the cavity member 20 may not include the first cooling fins 23 and thus the objective of the present invention may be achieved according to the thermo-chemically stable layer.

Although the rear cover 40 includes the second cooling fins 42 that protrude toward the cavity 22, extending in a direction perpendicular to a ground, and are spaced apart from each other in a direction perpendicular to the direction perpendicular to the ground in the present embodiment, the rear cover 40 may not include the second cooling fins 42 and thus the objective of the present invention may be achieved according to the thermo-chemically stable layer.

Although the through holes 52 have circular or hexagonal cross sections perpendicular to the path in which the protons are irradiated, and have a honeycomb shape cross section perpendicular to the path in which the protons are irradiated in the present embodiment, the present invention is not limited thereto, the through holes 52 may have rectangular and octagonal cross-sections and thus the objective of the present invention may be achieved.

A target apparatus of the present invention has formed a plating layer that thermo-chemically stabilizes an inner circumference of a cavity accommodating a nuclear reaction material, by which reduces temperature and pressure of the cavity, thereby increasing a production yield of a radioactive isotope and increasing life span of the target apparatus.

Further, the cavity of the present invention has a remarkably increased surface area contacting cooling water used to cool the cavity, thereby providing a radioactive isotope production target apparatus having improved cooling performance.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. 

1. A radioisotope production target apparatus having improved cooling performance comprising a cavity member including a cavity accommodating an O-18 water and producing F-18 through a nuclear reaction between the O-18 water and protons irradiated onto the O-18 water, wherein the cavity member includes a front aperture and a rear aperture disposed in opposite directions on a path in which the protons are irradiated and connected to the cavity so that the cavity has openings, the target apparatus comprising: a front membrane disposed to cover the front aperture; a rear cover disposed to cover the rear aperture; a front cooling member coupled to the cavity member to support the front membrane so as to prevent the front membrane from swelling due to an pressure increases in the cavity during the nuclear reaction, disposed on the path in which the protons are irradiated, and including a plurality of through holes extending in a direction the protons are irradiated; a central cooling member including a space for supplying cooling water around the cavity and coupled to the cavity member; and a rear cooling member coupled to the rear cover and allowing the cooling water to be supplied, wherein a thermo-chemically stable layer plated with titanium or niobium is formed in an inner circumference of the cavity.
 2. The target apparatus of claim 1, wherein the thickness of the thermo-chemically stable layer may be between about 1 μm and 10 μm.
 3. The target apparatus of claim 1, wherein the cavity is between about 5 mm and about 20 mm long along the path in which the protons are irradiated.
 4. The target apparatus of claim 1, wherein the cavity has a truncated cone shape having an inner diameter increasing from an upstream side to a downstream side along the path in which the protons are irradiated.
 5. The target apparatus of claim 1, wherein the cavity member comprises a plurality of first cooling fins that protrude from an exterior surface of the cavity, extend around the circumference of the cavity, and are spaced apart from each other in the direction in which the protons are irradiated.
 6. The target apparatus of claim 1, wherein the rear cover comprises a plurality of second cooling fins that protrude toward the cavity, extend in a direction perpendicular to a ground, and are spaced apart from each other in a direction perpendicular to the direction perpendicular to the ground.
 7. The target apparatus of claim 1, further comprising: a plurality of through holes having circular or hexagonal cross sections perpendicular to the path in which the protons are irradiated, and arranged in a honeycomb shape and having cross sections perpendicular to the path in which the protons are irradiated.
 8. The target apparatus of claim 1, wherein the front membrane is formed of titanium or niobium.
 9. The target apparatus of claim 1, wherein the plurality of second cooling fins are plated with titanium or niobium. 